I would say it's probably the onesie. A lot of people don't have luck with the cloth diaper/onesie combination!!

We've never had a problem with it, unless I'm using a prefold and a cover; but with fb's we've been fine.

Granted, my son is 15 months old, and we just packed away his 3-6 month onesies, he's finally graduated to 6-9 month ones!! He's pretty small, so I don't know if that makes a difference as to why we haven't had the onesie problem!